The overall goal of this project is to combine longitudinal and cross sectional methodologies to identify markers of cognitive decline in normally aging and dementing individuals. In addition to the longitudinal data on changes in temporal and spatial aspects of event-related potentials (ERPs), specific experiments will assess cognitive operations that are vulnerable in the elderly and those at risk for dementia: semantic activation, elaboration at encoding on memory tasks, and motor slowing. Event-related potentials (ERPs) will be recorded from the scalp, time locked to auditory and visual stimuli. The ERP waveform is expected to vary as a function of experimental condition, age, and cognitive impairment, thus providing measures of the timing and efficiency of cognitive processing in three groups of the aged: normal, high risk for dementia, and demented. A detailed scalp topographic analysis, utilizing the Laplacian method for reference free measurements of transcranial current flow, will provide an indication of age-related change in the differential intracranial generation of these ERP components.